WindowServer: Convert entire API to be message-based.

One big step towards userspace WindowServer. :^)

Kernel/Process.cpp

@@ -2133,7 +2133,6 @@ void Process::finalize()
 {
     ASSERT(current == g_finalizer);
 
-    destroy_all_menus();
     destroy_all_windows();
     m_fds.clear();
     m_tty = nullptr;